Room temperature fast-curable organopolysiloxane compositions of the condensation cure type which are known in the art include one-part compositions comprising a hydroxy-terminated organopolysiloxane as a base polymer and a crosslinker wherein the amount of the crosslinker is minimized to improve a crosslinking rate through hydrolysis, and two-part compositions wherein a hydroxy-terminated organopolysiloxane as a base polymer and a crosslinker are separately packed and mixed on use.
One-part compositions are not regarded fast-curable despite a high cure rate from the surface, because deep-section cure takes a certain time. It is believed that two-part compositions are effective where fast cure is of high priority. Although two-part compositions of the condensation cure type are relatively good in deep-section cure, they are cumbersome to handle and unamenable to automatic mixers or dispensers because two parts are mixed in a different volume ratio from 1:1. For complete cure to the depth, it is necessary to strictly determine the amount of crosslinker added relative to the amount of terminal hydroxy groups of organopolysiloxane or to add water as a deep-section curing agent.
On the other hand, organopolysiloxane compositions of the addition cure type are advantageous in working because two parts are mixed in a ratio of 1:1. However, heating ovens are usually necessary for curing. Also the working environment is limited since the curing catalyst can be poisoned in the presence of an addition poison.
JP 3916403 discloses a composition comprising a diorganopolysiloxane blocked at both ends of the molecular chain with hydrolyzable hydroxy groups, an organic compound having at least one carbonyl group (C═O) in the molecule, and an organic compound having at least one primary amino group (NH2) in the molecule. This composition is intended to improve deep-section cure and fast-cure by utilizing water produced additionally from ketimine-forming reaction between carbonyl and primary amino groups. Thus the composition is improved in deep-section cure and fast-cure. However, when heat is applied in the uncured state, the dialkylketoxime which is the condensation reaction product is quickly gasified whereby bubbles are introduced in the cured composition, bringing a substantial drop in sealing capability, which is undesirable particularly in the automotive oil-seal application. JP 3970484 overcomes the problem by limiting the type and amount of the curing agent so as to prevent bubble formation in the cured composition.
Although these patents propose an effective approach, a problem arises when this approach is applied to organopolysiloxane compositions of the dealcoholization type. The cure rate is slightly accelerated, but apparently slow as compared with the compositions of the deoximation type. Thus the approach is not applicable in the automobile and electrical and electronic industries where fast cure is required. Even when the conventional measure of adding water as the deep-section curing agent is employed for the purpose of improving cure, no dramatic improvement in cure is achieved.
Citation List
Patent Document 1: JP 3916403
Patent Document 2: JP 3970484